There are many definitions of religion most of which boil down to educated guesses. Some Western scholars contend that religion cannot be adequately defined. The dictionary meaning is one of many possible definitions which stretch from the practical such as worshiping a super human controlling power, to the theoretical in Schleiermacher’s, “All religion expresses itself in such an awareness of something outside and beyond nature.”
Curiously, the Sanskrit language has no equivalent for the word religion nor does the Sanskrit or Pali word dharma/dhamma find an equivalent in a European language such as English.
To the question, is Buddhism a religion? we could say, yes it is, but not in the sense of worshiping a god or some super controlling power. Strictly speaking, however, Buddhism is a dharma. Generally, dharma means ‘that which holds together or bears’, in the sense of an underlying unific reality. The teaching of Buddhism then, as a dharma, concerns the seeing of this reality so as to be in accord with it. Pausing here, the reader can see how the word religion and dharma don’t mesh very well.
We should also note that Buddhism is not, strictly speaking, a philosophy in the Western sense of the word, that is, a speculative attempt to present a complete systematic view of reality. Buddhism rests upon dharma. According to the Buddha, “this dharma is profound, of deep splendor, difficult to see, difficult to understand, incomprehensible, having the incomprehensible as its scope, fine, subtle, the sense of which can only be understood by the wise” (Catuṣpariṣat Sūtra). What the Buddha is describing is really the essence of reality rather than a systematic view of reality. This essence I hasten to add is unconditioned.
I know some Westerners have the bad habit of trying to put Zen Buddhism into the bag of philosophy. But it doesn’t fit. Zen is about dharma or the same, the true dharma (saddharma). This was reached by Siddhartha, the Buddha-to-be, through dhyana or meditation. This implies a high level of personal purification, not speculative powers able to concoct a system or model of reality.